Partial oxidation of hydrocarbons using gaseous sulfur trioxide



March 25, 1952 W. H. REEDER, IIJI PARTIAL OXIDATION OF HYDROCARBONS USING GASEOUS SULFUR TRIOXIDE Filed June 8, 1946 9 v 9 a 0 q mm w, Saw; a J NM N E INVENTOR. 1.1 -Zeedeafl Patented Mar. 25, 1952 PARTIAL OXIDATION OF HYDROCARBONS USING GASEOUS SULFUR TRIOXIDE William H. Reeder, III, Olean, N. Y., assignor to Clark Bros. 00., Inc.

Application June 8, 1946, Serial No. 675,372

Claims. (Cl. 260-604) This invention relates to the limited oxidation of hydrocarbons, and more particularly of the normally gaseous, saturated, aliphatic hydrocarbons, for the formation of oxygenated compounds and particularly of carbonyl compounds such as aldehydes and ketones. It is also applicable to the limited oxidation of other hydrocarbons such as benzene, and petroleum fractions.

An object of this invention is to prepare oxygenated compounds by oxidation of hydrocarbons in such a manner that the nature of the products formed may be controlled and limited, preferably to carbonyl compounds such as aldehydic and ketonic compounds in the main. A further object of this invention is to provide a process for the oxidation of hydrocarbons wherein the yields of such oxygenated compounds are high and their number is relatively small, and whereby such compounds may be easily separated in relatively pure form from the products of reaction. Other objects of this invention will appear from the following detailed description.

In previously known processes the partial oxidation of the normally gaseous, aliphatic hydrocarbons is accomplished by contacting with oxygen or with free oxygen-containing gas. The number of oxygenated products formed in such processes is large. A- series of products which includes the corresponding aliphatic alcohols, aldehydes and ketones, carboxylic acids and the oxides of carbon is formed for each hydrocarbon being oxidized. Such mixtures of products are generally very difficult to separate into commercially pure components. Moreover, in such processes, because the intermediate products are generally more easily oxidized than the hydrocarbons, it is difiicult to prevent the formation of considerable quantities of the oxides of carbon, with the result that the amount of hy drocarbon converted to useful products is relatively small. Such control as is exercised in the yield and number of products formed is obtained through the use of catalyst, a diluent, short contact time Or a special method of contacting or cooling.

A process in which higher yields and simple aldehydic products are obtained by the limited oxidation of the normally gaseous, saturated, aliphatic hydrocarbons is disclosed in the application of Fredlee M. McNall, Serial No. 548,694, filed August 9, 1944 now Patent Number 2,532,930. In this process, sulfuric acid, in the absence. of oxy-.- gen and of free oxygen-containing gas, is employed as the oxidizing agent. The reaction may be conducted in the presence of liquid sulfuri acid at high temperatures and preferably, but not necessarily, in the presence of a catalyst dissolved in the hot sulfuric acid.

It has been found that in carrying out the reaction as disclosed in the aforesaid McNall applications, in which the hot sulfuric acid acts as the oxidizing agent, that although the amount of hydrocarbons converted to aldehyde is large, there is a high consumption of the sulfuric acid and. a correspondingly high production of sulfur dioxide, resulting in a high cost of operation. Furthermore, the process, when conducted under conditions to secure effective yields of formaldehyde from the methane in mixtures of hydrocarbons such as occurs in natural gas, does not oxidize the higher hydrocarbons present with good yields of aldehydic products.

I have new found that by using gaseous. sulfur trioxide as the oxidizing agent, and in the pres.- ence of a catalyst consisting of a suitably pre pared or activated adsorptive material, that methane, its homologues and other hydrocarbons may be partially oxidized with a much more efiec-- tive utilization of the oxidizing agent than when liquid sulfuric acid with or without a dissolved catalyst is used.

The course of the reaction appears to be as follows: two molecular equivalents of sulfur trioxide react in the presence of an appropriate catalyst with one of hydrocarbon to yield one equivalent of the corresponding aldehyde or ketone, one of water and two of sulfur dioxide.

The temperatures employed are generally in the order of 450 C., the preferred temperatures varying with the hydrocarbons used.

When the reaction is conducted according to the present invention as hereinafter described, not only is the hydrocarbon converted to a single. product or a simple, easily separablemixture in good yield, but also the amount of sulfur trioxide converted to the dioxide is not excessive. V

The process employing the gaseous sulfur tri oxide oxidant in accordance with the present invention has marked advantages over that using hot liquid sulfuric acid, even with a catalyst. Thus, when liquid sulfuric acid is used, the amount of catalyst which can be used is relatively small and is limited to the amounts of salts, metals, oxides that are soluble in the hot acid. In the vapor-phase process, a very considerably more effective amount of catalyst in the ,form of a suitably prepared adsorptive material can be placed inthe reaction zone.

In the process using the liquid acid, the con centration of sulfuric acid and sulfuric acid vapor in the reaction zone is high with respect to that of the hydrocarbon present and may be varied only within a narrow range of relatively high concentrations. In the vapor-phase process, the concentration of sulfur trioxide in the hydrocarbon gas being treated can be varied independently over a wide range and thus the most favorable oxidant concentration for the conversion of hydrocarbon to aldehyde can be utilized.

Further advantages are inherent in the use of the vapor-phase process of the present invention. I

Minor variations in temperature and pressure not only do not so markedly influence the effectiveness of the gaseous sulfur trioxide oxidant as they do that of the liquid acid oxidant, and such variations are much more easily avoided. Furthermore, corrosion problems incidental to the handling of relatively large quantities of hot concentrated liquid sulfuric acid are appreciably diminished by the use of lesser quantities of hot gaseous sulfur trioxide.

Adsorptive catalytic materials of widely varying types may be used and it appears that the important characteristic from the standpoint of the desired reaction is their highly adsorptive character rather than their specific chemical composition, although minor variations in behavior result from the latter. Thus, widely varying adsorptive materials may be employed, such as charcoal, silica gel, alumina, fullers earth, bauxite, kieselguhr, aluminum silicates, hydrated aluminum or magnesium silicates, and the like. It will be appreciated that in some cases, particularly of natural minerals, the adsorptive material may be treated preliminarily with sulfuric acid to improve its adsorptive and catalytic action.

As hereinbefore stated, such adsorptive materials of widely varying character may be employed with only minor specific differences in operation. Thus, with charcoal, given yields of formaldehyde are attained from the oxidation of methane at somewhat lower temperatures than with other adsorptive materials named, but there is also a tendency to form oxides of carbon in the reaction at lower temperatures than with non-carbonaceous adsorptives, such as alumina and silica gel. Consequently when charcoal is employed, the differential between the temperatures for optimum formaldehyde formation and those for the formation of carbon oxides is less and a more careful control of temperature of operation is required. With alumina, for example, this differential is somewhat greater. Silica gel appears to favor the reduction of the sulfur oxides to free sulfur, as compared with other adsorptive materials.

Metallic salts or oxides which promote or catalyze oxidation of hydrocarbons may be deposited on the adsorptive material to increase the effectiveness of the limited oxidation of hydrocarbons and to aid in reducing the production of oxides of carbon. Suitable for this purpose are the salts and oxides of the elements of the Ib periodic group and the transition elements and mixtures thereof. The transition elements include the metals Sc, Ti, V, Cr, Mn, Fe, Co and Ni in the 4th long series, Y, Zr, Nb, Mo, Ma, Ru, Rh and Pd in the 5th long series, La, Ce and the other rare earths, Hf, 'Ia, W, Re, Os, Ir and Pt in the 6th long series and Ac, Th, Pa and U in the 7th long series. It will be noted that in the long period arrangement of the elements and in the Bohr classification the elements of the 1b group, viz., Cu, Ag and Au, follow immediately the transition elements in their respective series and share with them the property of variable valency. See, for example, Ephraim, Inorganic Chemistry, 4th ed, revised, New York, 1943, pages 25 and 29.

When the metallic salts are employed, soluble salts of the selected metal or mixture of metals may be dissolved in water and the resulting solution thoroughly mixed with the adsorptive material, which is then dried and heated as hereinafter described. The particular salt which is employed does not appear to affect the reaction. Thus, chlorides, nitrates, sulfates, acetates or the like may be employed, providing they are sufficiently soluble to permit of securing the desired proportion of the metallic salt or salts in the adsorptive material.

Irrespective of whether the adsorptive material does or does not contain a metallic salt, its effectiveness may frequently be increased by a preliminary heat treatment or activation, which may be carried out either before or after the catalyst has been placed in the reaction chamber in which it is to be used. This treatment is effected by heating the adsorptive material, with or without added metal compound, at a high temperature, in the order of 400 to (500 C. or higher. The optimum temperature of activation for each adsorptive material or catalyst combination may vary Within this range and may be selected on the basis of prior experiment or test. Good results are secured by heating the adsorptive material While passing through the chamber containing it a stream of air, of sulfur oxides, of the hydrocarbon gas to be oxidized, orof mixtures thereof, providing of course, that if a hydrocarbon be present, the activation temperature does not exceed the cracking temperature of the hydrocarbon. Only a short period of heat treatment is required, say to 1 hour, longer treatment doing no apparent harm, and in some cases being advantageous, as with alumina. The heat treatment may suitably be efi'ected at the beginning of an operation, While passing hydrocarbons alone, air or inert gas through the reaction system and before beginning the introduction of sulfur trioxide. In reactivating catalyst which has become spent or partially spent in use, a similar heat treatment is applied, in which air should be used.

In carrying out the reaction, the hydrocarbon gases and sulfur trioxide may be mixed in desired proportions prior to entering the reaction zone or they may be simultaneously introduced into the latter in the desired proportions. Thus, when sulfuric acid is used as the source of the sulfur trioxide or sulfuric acid vapors, it may be placed in a heated chamber or boiler and the hydrocarbon gas passed through it, the proportion of the sulfuric acid vapor carried away by the gas being controlled by varying the temperature to which the sulfuric acid is heated. The mixture of gas and sulfuric acid vapor then passes to the reaction chamber, which is maintained under the desired reaction conditions. Instead of passing the hydrocarbon gas through the acid, the acid may be passed into a separate vaporizing chamber in amounts to give the de sired concentration of sulfuric acid vapor, and the resulting vapors passed into the reaction chamber simultaneously with the hydrocarbon gas. Sulfur trioxide gas may be employed instead of sulfuric acid vapors, if desired.

The proportion of sulfur trioxide introduced, generally as sulfuric acid vapor, is preferably substantially in excess of that required for the oxidation of the hydrocarbon which is to be oxidized in a single pass through the reaction chamber. Since, in general, it has been found preferable to oxidize only a small proportion of the hydrocarbon gas per pass and to use a recycling system, it has been found satisfactory to supply a quantity of sulfuric acid sufficient to secure about 0.2 to 15% of $03 in the total gas, including recycled gas, if any, entering the reaction chamber. When the sulfuric acid or $03 is supplied by passing the gas through heated sulfuric acid before entering the reaction chamber, the proportion of sulfuric acid supplied may be controlled by varying the temperature to which the sulfuric acid is heated. This temperature may be in the order of 250 to 350 0., although for, best yields, relative to sulfuric acid consumed, of formaldehyde from the oxidation of methane temperatures of 250 to 280 C. are preferred. Sulfur dioxide, although not necessary for the oxidation will usually be present in any recycling operation. In small amounts it may be beneficial, apparently in the direction of limiting the extent of oxidation. The operation is controlled so that the proportion of sulfur dioxide in the cycle gas does not exceed 50% to 60% and preferably is not more than 20%. Oxygen or free-oxygen containing gas is not added.

The reaction chamber which contains the adsorptive catalytic material, either with. or without added metallic salts, is maintained at a temperature of from 175 to 450 C. In the treatment of methane, the most effective oxidation of the hydrocarbon gas is secured with good yields of formaldehyde relative to the hydrocarbon consumed at a temperature of 325 to 425 C. Within the ranges set forth, the more effective utilization of both hydrocarbon and acid is secured with good yields of oxygenated products based on hydrocarbon consumed when lower proportions of sulfur trioxide are used.

The gases leaving the reaction chamber, which contain the desired oxygenated compounds, the sulfur dioxide resulting from the reaction un reacted hydrocarbon and sulfur trioxide, as well as any oxides of carbon that may be formed, are passed through a cooler and any resulting condensate is collected. The cooled vapors are then passed through a scrubber in which they are scrubbed with water or with other suitable fluid, as described, for example, in my copending application Serial No. 676,469, filed June 13, 1946. In the scrubber the desired oxygenated compounds are removed from the vapors, together with unreacted sulfur trioxide and some of the sulfur dioxide. The resultin solution is passed through a suitable product still from which the desired oxygenated compounds are recovered.

The recycle gas leaving the scrubber, which includes unreacted hydrocarbons and sulfur dioxide, is then returned to the reaction chamber, make up gas being added to compensate for the hydrocarbon consumed.

With the higher concentrations of sulfur dioxide in the reacting gases, say from 20% to 60%, there is a greater tendency for the formation of free sulfur and hydrogen sulfide than when concentrations of sulfur dioxide of less than 20% are maintained. When such high sulfur dioxide concentrations obtain, the formation of excessive amounts of free sulfur and hydrogen sufide may be avoided by the use of lower temperatures at which the yields per pass of formaldehyde, aldehydic or oxygenated products relative to the amount of methane or'other hy drocarbon gas passing through the reaction zone are, however, somewhat reduced.

The homologues of methane, as well as benzene, and gasoline fractions which are in the gaseous state at reaction temperature, may be similarly converted to partially oxygenated products under the broad ranges of conditions above recited. There is, however, for each hydrocarbon, an optimum reaction temperature range within the broad range heretofore referred to which is not necessarily the same as that used for the partial oxidation of methane. For example, ethane is oxidized in good yield to acetaldehyde preferably at temperatures of 270 to 350" 0., and butane to butyraldehyde and ketones at temperatures of to 300 C. Optimum reaction temperatures for the partial oxidation of the higher homologues are correspondingly lower. Benzene may be effectively oxidized to yield phenol in substantially the same temperature range preferred for the partial oxidation of methane.

Apparatus suitable for carrying out the invention is illustrated in the accompanying drawing in which a flow sheet of apparatus suitable for carrying the invention into effect is shown diagrammatically.

Referring to the drawing, the numeral I0 designates a heated chamber or tower to which sulfuric acid may be supplied through the valve controlled line II. It is heated in any suitable manner; for example, it may be jacketed and a heated high-boiling fluid, such as diphenyl or diphenyl oxide, circulated through the jacket by means of lines l2 and I3.

The chamber or acid vaporizer in may, if desired, be provided with an inert packing, such as carbon rings, porcelain, stoneware or the like (not shown) to distribute the acid and facilitate its vaporization. The acid vaporizer I0 is connected by line I 4 to the reaction chamber I5, into which is charged the inert adsorptive material. Suitable means are provided for applying heat to or removing heat from the reaction chamber 15; for example, it may be jacketed and a suitable heated heat transfer fluid, such as diphenyl or diphenyl oxide or a fused salt mixture, may be circulated through the heating jacket by means of the lines It and H. As is apparent, any suitable catalyst casing provided with heating and temperature control means, as known in the art, may be employed.

Hydrocarbon gas, together with recycled gases from the system, are introduced into the reaction chamber i5 through the line l8 and line H.

The reacted gases containing the desired'oxygenated compounds pass out of the reaction chamber l5 through line 29 and pass through a suitable cooler 20. The cooled gases, together with any condensate formed therefrom, pass out of the cooler 20 through the line 2| into-the receiver 22. Any liquid collected in receiver 22 may be withdrawn through line 23 and, if found to contain appreciable quantities of formaldehyde or other oxygenated products, may be transferred to a product still, not shown.

Uncondensed vapors and gases, which contain aldehydic or other limited oxidation products formed, pass out of the receiver 22 through line 24 into a scrubbing column 25, in which they are scrubbed with water or other suitable fluid and the greater part or substantially all of the desired oxygenated products contained in the gases are removed from them. The scrubbing liquid may be supplied to the scrubber 25 through line 26. The scrubbing tower 25 may be of any suitable type; for example, a packed tower or a bubble plate tower. The scrubbing liquid, in passing through the tower, removes, in addition to aldehydic and other limited oxidation products, part of the sulfur dioxide and sulfur trioxide contained in the gases and vapors, together with other products of reaction that may be formed, such as acids, carbon dioxide and the like. The scrubbing liquid leaves the scrubbing tower 25 through the line 21 and is transferred to the product still (not shown), in which the oxygenated products and sulfur dioxide are removed.

The vapors and gases leaving the scrubbing tower 25, which contain sulfur dioxide and water vapor in addition to unreacted hydrocarbons, traces of aldehyde and other oxygenated products and other inert gaseous materials, pass through line 28 into a second scrubbing tower 29, which may suitably be a packed tower and in which traces of valuable oxygenated products are removed. If desired, this tower may also be used as a drying tower in which the gases are dried, for example, by scrubbing with concentrated sulfuric acid, supp-lied through the line 30, or other suitable drying means may be used.

The gases then pass through line 3i into the recycling line 32, by which they are conducted to the compressor or blower 33, by which they are forced into the line E3 to return to the reaction chamber l5. The make-up of fresh hydrocarbon gas may be supplied through the line 34 to line i8, through which it is conducted to the reaction chamber.

In the event of the excessive accumulation of nonreactive or undesirable gases in the system, a vent line 35, controlled by a suitable valve 36, is provided to permit partial or complete venting of the system.

The system as above described is adapted for recycling operation. In case it is desired to use it for once-through or single pass operation, the recycling line 32 and the compressor or blower 33 may be cut out of the system by closing the valves 31 and 38, fresh hydrocarbon gas being then supplied continuously through the line 34 and the efiluent gases from the scrubber 29 being discharged continuously through the line SI and the vent line 35.

In carrying out the process, the hydrocarbon gas employed is one consisting largely of the hydrocarbons which it is desired to oxidize into aldehydes. For the production of formaldehyde, the gas should be one consisting largely or en tirely of methane. Thus natural gas may be employed. or substantially pure methane gas, or mixtures of methane and hydrogen derived from natural gas. It has been also found that gas prepared for illuminating and heating purposes and consisting largely of methane may be used, even though such gas contains varying proportions of other constituents derived from coal gas, water gas or the like. In general, it is preferred that the methane content of the gas used be in the order of 75% or higher. The higher aliphatic hydrocarbons such as ethane, propane and the like and also the cyclic and aromatic hydrocarbons may be oxidized to partially oxygenated products, primarily aldehydic and ketonic by the process of the present invention. I v

The reaction chamber is charged with a suitable inert adsorptive material which, as herein} before set forth, may be of widely varying types, such as charcoal, silica gel, alumina, fullers earth, bauxite, kieselguhr, aluminum silicate or the like. For purposes of illustration, examples of operation with certain of these will be given, but it has been found that the others may be employed, the principal requisites being that the material employed shall be adsorptive and shall not be decomposed at the temperatures employed by the hydrocarbons and the sulfur oxides present.

In some cases the eiliciency of the reaction may be improved by incorporating in the adsorptive material salts or oxides of the metals of the Ib periodic group and of the transition elements or mixtures thereof. For example, in addition to salts of others of such metals, silver, copper, molybdenum, cerium, iron, cobalt, nickel and platinum salts have been employed as well as mixtures of them, such as mixtures of cobalt and silver salts, cobalt and copper salts, cobalt and molybdenum salts, and the like. These metal salts modify the reaction in various ways; in some cases by lowering the temperature at which most efiicient reaction takes place and in other cases by reducing the losses through excessive oxidation of the hydrocarbons present or excessive reduction of the sulfur oxides to sulfur and hydrogen sulfide.

When the metallic compounds are used, the particular salt or compound employed does not appear to be material. It may be dissolved in the form of a soluble salt and deposited upon the adsorptive material by evaporation or by precipitation as oxide or other insoluble compound. The amount employed may suitably be from 1 to 25% and preferably from 2 to 10%, based on the amount of the adsorptive material. Thus the sulphates, chlorides, nitrates, acetates, formates or other soluble salts of the metals may be used. In general, when deposited by evaporation, the inorganic salts are preferred, since they do not leave a carbonaceous residue when the mixture with the adsorptive material is heated to drive off moisture and to activate the mixture, or during reaction.

In order that the adsorptive material, either with or without added metallic compound, shall have the desired eifectiveness, it has been found advantageous to activate it. This is accomplished by heating the adsorptive material, with metallic compound if that is present, to a high temperature in the order of 400 to 600 C. or higher in the presence of either air, methane or other hydrocarbon to be used in the reaction. This may suitably be done at-the beginning of an operation by charging the adsorptive material, with or without added metal compound into the reaction chamber, heating it to a temperature of 400 to 500 (3., preferably about 450 C., and passing the hydrocarbon gas alone through it for a sufi'icient period of time to bring the adsorptive material to an active state. A heat treat: ment from to 1 hour, after the adsorptive material has become heated throughout its entire mass, is sufiicient for this purpose. A longer period of heating may be employed, if desired, say from 3 to 5 hours, and does not impair the activity of the resulting contact mass and in some cases, improves it. Other methods of activation known in the art may be employed.

In carrying out the reaction, the activated con.- tact 'mass, which may include metallic com: pounds, is maintained at the desired temperature in the reaction chamber I 5 by circulating a suitgum-r24 able heat transfer fluid, such as diphenyl or diphenyl oxide, through the heating space therein. The hydrocarbon gas is supplied through the lines 34 and I8 and sulfur trioxide is supplied suitably in the form of vaporized sulfuric acid from the acid vaporizer I0.

The adsorptive material in the reaction chamber is maintained at a temperature of 250 to 450 C. and preferably at a temperature of from 325 to 425 C. when methane is the hydrocarbon being treated. The operation may be conducted as a once-through operation but inasmuch as it is found that the best yields of the partial oxidation products can be secured on the basis of the hydrocarbon consumed by operating with a relatively low yield per pass, generally below about 2% and suitably about 0.2 to 1%, it is preferred to recycle the outgoing gases after removal of the aldehydes and other oxygenated compounds therefrom. These efliuent gases contain unreacted hydrocarbons, sulfur dioxide, and sulfur trioxide besides any inert gases that may be present, such as hydrogen, nitrogen or the like.

In carrying out the operation, the proportion of sulfur trioxide in the mixture entering the reaction chamber may vary quite widely, as may also the proportion of sulfur dioxide. The proportion of sulfur trioxide in the gases supplied.

to the reactor may range from about 0.2% to 15% and in general it is preferred that it be in the range from 1.5% to 6%. As hereinbefore referred to, the proportion of sulfur dioxide present may be as low as in single pass operation, although it may be found desirable to add sulfur dioxide in such case; and in recycling operation the proportion of sulfur dioxide may reach as high as 60%.

In carrying out the reaction, it has been found that there are certain side reactions which reduce the efficiency of the process by wastage of sulfur oxides and of hydrocarbon, among these being the reduction of the sulfur oxides to sulfur and hydrogen sulfide, and the oxidation of the hydrocarbon to carbon monoxide and carbon dioxide. These side reactions do not decrease the effectiveness of conversion of hydrocarbons to oxygenated compounds; on the contrary, they are frequently accompanied by much greater overall yields of limited oxidation products. However, since they result in a waste of reagents, it may be found desirable to conduct the operations so as to limit them. While highly effective production of the desired limited oxidation products is obtained with a sulfur dioxide content in the gas fed to the reactor up to as high as 60%, in order to minimize the losses of sulfur oxides by reduction to sulfur and hydrogen sulfide it has been found advisable not to allow the sulfur dioxide content of the gas used to exceed about 20%.

It will be apparent that, when economic considerations are such that losses of sulfur oxides through excessive reduction can be disregarded,

proportions of sulfur dioxide in the higher range may be used.

As hereinbefore set forth, a wide range of adsorptive materials may be used, and specific ones have been referred to which are of various types; for example, carbonaceous, silicious and aluminiferous. The effectiveness of these materials appears to result primarily from their adsorptive characteristics and apparently any sufficiently inert highly adsorptive material may be em ployed. However, there are certain differences in the behavior of individual adsorptive mate- 10 a rials. All of them are effective in the range of temperatures hereinbefore set forth, but their optimum activity may appear in different parts of the range. Thus, with activated carbon or other carbonaceous adsorptive material, a high rate of reaction to produce formaldehyde from the limited oxidation of methane is secured at considerably lower temperatures within the range than with alumina or similar alumina-containing material. With silicious material such as silica gel, the optimum reaction conditions are secured with temperatures intermediate between those for carbon and for alumina but the efiiciency of the activated silica gel is somewhat less than that of the other adsorptive materials containing carbon and alumina.

The adsorptive materials also differ somewhat in their behavior in respect of side reactions. Thus, with activated carbon, the temperature at which excessive reduction of the sulfur oxides to sulfur and hydrogen sulfide takes place is likewise lower than in the case of alumina and the spread between the temperatures for optimum production of the desired oxidation products and for excessive reduction of sulfur oxides is less in the case of carbon than in the case of alumina,

' silica gel standing between the two in these respects. Consequently, although specific temperatures for optimum results within the range indicated may besomewhat lower with carbonthan with alumina, when the former is used a somewhat more careful control of the operation is required.

Furthermore, the added metallic compounds, such as the salts or oxides which have been referred to hereinbefore vary somewhat in their effects upon different inert adsorptive materials, all of them being found to have a beneficial effect either in the direction of promoting the formation of the desired limited oxidation prod-- ucts or of minimizing the side reactions. Thus, the addition of cerium salts to activated carbon does not apparently increase the formation of the desired oxidation products at a given temperature, but does appear to reduce the extent of reduction of the sulfur oxides to sulfur and hydrogen sulfide. With both silica gel and alumina similar amounts of cerium appear to increase the yield of the desired oxidation products based on hydrocarbon consumed at a given temperature or to permit the use of somewhat lower temperatures for equivalent rates of production of the desired oxidation products. Similar variations have been found in the effects of the other metallic promoters.

The following examples are illustrative of operations conducted in accordance with the present invention. In these examples the term apparent contact time is used to indicate the reciprocal of the space velocity (volumes of gas at standard temperature and pressure circulated per hour per unit Volume of contact mass) converted to a time base of seconds. As will be apparent, in operations conducted under pressure the apparent contact time must be correlated to the pressure used.

Example 1 1 A gas containing about 97% methane, 0.7% S03, 0.5% S02, and 1.8% carbon monoxide and dioxide was continuously recirculated through a reaction chamber filled with adsorptive material consisting of activated alumina containing 1% cobalt sulfate and 0.02% silver nitrate on a weight basis. The adsorptive material was maintained at a temperature of 330 C. The rate at ,hyde (as a gas at standard temperature and pressure) per hour per unit volume of catalyst was 0.44.

Example 2 A gas containing about 880% methane, 6% of the higher homologues of methane, 1.2% S03, 2% S02 and 10.8% carbon oxides and nitrogen was continuously recirculated through a reaction chamber filled with activated alumina upon which by weight of ceric sulfate had been deposited. The adsorptive material was maintained at a temperature of 350 C. The rate at which the gas was passed through the adsorptive material was such that the apparent contact time was 11.2 seconds.

The molar yield of formaldehyde based on hydrocarbon consumed was 66%. The molar yield of formaldehyde based on sulfur trioxide consumed was about 60%. Considered on a single pass basis, the volume yield of formaldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst was 0.5.

Example 3 A gas containing about 73% methane, 5% higher homologues, 4% S03, 4.5% S02, the balance being carbon oxide, hydrogen, and nitrogen, was continuously recirculated through a reaction chamber filled with activated alumina containing 1% by Weight of cobalt sulfate and 4% by weight of copper sulfate. The adsorptive material was maintained at a temperature of 390 C. The apparent contact time was 13.1 seconds.

The molar yield of formaldehyde based on hydrocarbon consumed was in excess of 42%. Considered on a single pass basis, the volume yield of aldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst was 0.225.

Example 4 A gas containing about 41% methane, 5% higher homologues, 2% S03, 8% S02, the balance being carbon oxides, hydrogen, and nitrogen, was continuously recirculated through a reaction chamber filled with activated charcoal. The absorptive material was maintained at a temperature of 375 C. The apparent contact time was 12 seconds.

The molar yield of formaldehyde based on hydrocarbon consumed was in excess of 66%. Considered on a single pass basis, the volume yield of aldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst was 0.53.

Example 5 A gas containing about 56% methane, 4% higher homologues, 2% S03, 28% S02, the balance being carbon oxide, hydrogen, and nitrogen, was continuously recirculated through a reaction chamber filled with activated charcoal containing by weight of ceric sulfate. The adsorptive material was maintained at a temperature of 330 C. The apparent contact time was 7.73 seconds.

The molar yield of formaldehyde based on hy- 12 drocarbon consumed was in excess of 69%. Considered on a single pass basis, the volume yield of aldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst Was 0.705.

Example 6 A gas containing about 74% methane, 5% higher homologues, 3.5% S03, 2% S02, the balance being carbon oxide, hydrogen, and nitrogen, was continuously recirculated through a reaction chamber filled with activated silica gel containing 5% by weight of ceric sulfate. The adsorptive material was maintained at a temperature of 400 C. The apparent contact time was 12.97 seconds.

The molar yield of formaldehyde based on hydrocarbon consumed was in excess of 53%. Considered on a single pass basis, the volume yield of aldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst was 0.30.

Example 7 A gas containing about 96% ethane, 0.8% S03, 0.2% S02, the balance being carbon oxide, hydrogen and nitrogen was continuously recirculated through a reaction chamber filled with activated alumina containing 0.5% by weight of cobalt sulfate. The adsorptive material was maintained at a temperature of 300 C. The apparent contact time was 0.72 second.

The molar yield based on ethane consumed of partially oxygenated products consisting of about 90% acetaldehyde and 10% formaldehyde, was in excess of 88%. The molar yield of aldehyde based on sulfur trioxide consumed was about 80%. Considered on a single pass basis, the volume yield of aldehydes (as gases at standard temperature and pressure) per hour per unit of volume of catalyst was 0.34.

Example 8 A gas containing about methane, 5% higher homologues, 4% S03, 2% S02, the balance being carbon oxide, hydrogen, and nitrogen, was continuously recirculated through a reaction chamber filled with activated silica gel. The adsorptive material was maintained at a temperature of 330 C. The apparent contact time was 6.28 seconds.

The molar yield based on hydrocarbon consumed of formaldehyde was in excess of 42%. Considered on a single pass basis, the volume yield of aldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst was 0.113.

Example 9 A gas containing about 65% methane, 4% higher homologues, 16% S03, 2% S02, the balance being carbon oxide, hydrogen, and nitrogen, was continuously recirculated through a reaction chamber filled with activated silica gel. The adsorptive material was maintained at a temperature of 400 C. The apparent contact time was 30.6 seconds.

The molar yield based on hydrocarbon consumed of formaldehyde was in excess of 45%. Considered on a single pass basis, the volume yield of aldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst was 0.4225.

Example 10 A gas containing about 93.4% iso-butane, 0.3% S03, 1% S02, the balance being carbon oxide,

"13 hydrogen, and nitrogen was continuously recirculated through a reaction chamber filled with activated alumina containing 0.5% by weight of cobalt sulfate. The adsorptive material was maintained at a temperature of 185 C. The apparent contact time was 0.73 second.

The molar yield of aldehyde, principally isobutyraldehyde, based on iso-butane consumed, was in excess of 58%. Considered on a single pass basis, the volume yield of aldehyde (as a gas at standard temperature and pressure) per hour per unit of volume of catalyst was 0.246. Employing the several adsorptive materials previously described, similar operations were conducted at various temperatures throughout the temperature range hereinbefore specified with effective conversion to aldehydic compound of the hydrocarbon content of the gas. In these, the proportions of sulfur trioxide in the gas fed to the reaction chamber varied from 0.7 to those of Sulfur dioxide from 0.2 to 50%; and those of hydrocarbon and inert gases from 47 to 97%. The molar yields of formaldehyde based on hydrocarbon consumed varied from 40% to over 90%, and based on sulfur trioxide consumed from to over 80%, and the volume yield of formaldehyde per hour per unit volume of catalyst varied from 0.05 to about 1.4.

Using activated carbon there was evidence of reduction of sulfur oxides to sulfur, greater at the upper range of temperatures, say at 375 to 400 C. and higher. More especially was this the case with high sulfur dioxide concentration, say above 20%. Although the overall production of aldehyde relative to hydrocarbon consumed was not appreciably increased by impregnation of the activated carbon with the metallic compounds hereinbefore named, the excessive reduction of sulfur oxides was reduced or eliminated, especially in the lower temperature range, say below 350 C.

Using activated silica gel, the activity at a given temperature with respect to production of aldehydic compound from the hydrocarbon was less at corresponding temperatures than with activated carbon. At higher temperatures there was an increased yield of formaldehyde per unit volume of catalyst, but this was apparently at the expense of efficiency since there was also greater formation of carbon oxides and a lower ratio of yield of formaldehyde to hydrocarbon consumed.

The addition of metallic promoters to the silica gel, in general, effected some reduction in the formation of carbon oxides and increased overall production of aldehydic compound rela-- tive to hydrocarbon consumed but did not increase the rate of production at a given temperature.

When activated alumina was used, the temperatures required to secure similar rates of conversion were in general higher than with activated-carbon. On the other hand, with activated' alumina, there was no evidence of excessive reduction of sulfur oxides to sulfur or hydrogen sulfide until temperatures of 400 C. and higher were reached.

Addition of varying proportions of metallic promoters to activated alumina did.not materially affect rates of formaldehyde production. However, the effectiveness of the utilization of sulfur trioxide was apparently increased as indicated by greatly increased yield of formaldehyde relative tov sulfur dioxide on a molar basis.

With activated alumina, as with silica gel,

somewhat higher. temperatures are required for a given yield of aldehydic compound than with carbon, but the tendency to form oxides of carbon is decreased.

The various metallic compounds employed as catalysts or promoters are effective individually or in admixture with each other. Thus compounds of the metals of the ID periodic group, copper, silver and gold, may be employed individ ually with the adsorptive material or carrier. However, it is preferred that they be used in admixture with compounds of the transition elements, as hereinbefore referred to. Compounds of the said transition elements may be used individually or in admixture or admived with one another or with compounds of copper, silver or gold.

In the reactions above described methane, ethane and butane were employed. In operaations under similar conditions, in accordance with the present invention, the higher homologues of methane are likewise converted into partially oxygenated products, in the main aldehydes and ketones with effective utilization of the hydrocarbon. These effective results have been secured with the various adsorptive mtaerials above set forth, both with and without the metallic promoters, in the oxidation of ethane, propane and the butanes to partial oxidation products, mainly aldehydic and ketonic in character. They are effective throughout the same tempera ture range as is used in the production of formaldehyde from methane although, in general, optimum conversions are secured at somewhat lower temperatures as the number of carbon atoms in the hydrocarbon increases. Of the adsorptive materials used, alumina appears to present the optimum conditions for conversion of the hydro carbons higher than methane.

Operation under varying conditions-has been hereinbefore described. To determine optimum conditions for the production of the desired limited oxidation products, it has been found most convenient, suitably in pilot equipment, to gradually increase the temperature of reaction within the ranges above set forth until either sulfur formation resulting from reduction of sulfur oxides or carbon oxide formation resulting from excessive oxidation of hydrocarbons becomes apparent, and then reducing the reaction temperature until formation of sulfur or carbon oxides disappears. The temperature may then be held constant until some change is required as a result of changes in composition of gas treated, or in the proportions of the reacting materials within the ranges above set forth.

Theprocess described can be carried out at pressures above atmospheric with beneficial results.

Although the present invention has been described in connection with the specific details of various embodiments thereof, it is not intended thereby to limit the invention except insofar as they may be included in the accompanying claims.

I claim:

1. The method of oxidizing saturated aliphatic hydrocarbon gases to form partially oxygenated compounds containing residual hydrogen including compounds containing the carbonyl group which comprises admixing such gases with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising an adsorptive catalytic material of the class consisting of adsorptive carbonace'ous, silicious and aluminiferous materials while maintaining a temperature in the range from about 175 to about 450 C.

2. The method of oxidizing saturated aliphatic hydrocarbon gases to form partially oxygenated compounds containing residual hydrogen including compounds containing the carbonyl group which comprises admixing such gases with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising activated charcoal while maintaining a temperature in the range from about 175 to about 450 C.

3. The method of oxidizing saturated aliphatic hydrocarbon gases to form partially oxygenated compounds containing residual hydrogen including compounds containing the carbonyl group which comprises admixing such gases with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising activated alumina while maintaining a temperature in the range from about 175 to about 450 C.

4. The method of oxidizing saturated aliphatic hydrocarbon gases to form partially oxygenated compounds containing residual hydrogen including compounds containing the carbonyl group which comprises admixing such gases with sulfur trioxide in vaporform in the absence of free oxygen and contacting the mixed gases with a contact mass comprising silica gel while maintaining a temperature in the range from about 175 to about 450 C.

5. The method of oxidizing saturated aliphatic hydrocarbon gases to form partially oxy- :2"

taining a temperature in the range from about 1 175 to about 450 C.

6. The method of oxidizing saturated aliphatic hydrocarbon gases to form partially oxygenated compounds containing residual hydrogen including compounds containing the carbonyl group which comprises admixing such gases with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising an adsorptive carrier, a compound of a transition element and a compound of an element of the Ib periodic group while maintaining a temperature in the range from about 175 to about 450 C.

7. The method of oxidizing methane to produce formaldehyde which comprises admixing methane with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising an adsorptive catalytic material while maintaining a temperature in the range from about 250 to about 450 C.

8. The method of oxidizing methane to produce formaldehyde which comprises admixing methane with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising an adsorptive catalytic material while maintaining a temperature in the range from about 325 to about 9.v The method of oxidizing methane to produce formaldehyde which comprises admixing methane with sulfur trioxide in proportions to provide from 0.2 to 15% of sulfur trioxide in vapor form in the mixture, and contacting the mixed gases with a contact mass comprising an adsorptive catalytic material while maintaining a temperature in the range from about 325 to about 425 C.

10. The method of oxidizing methane to produce formaldehyde which comprises admixing methane with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising an adsorptive carrier and a compound of the metal of the class consisting of the transition elements and the elements of the 127 periodic group, While maintaining a temperature in the range from about 250 to about 450 C.

11. The method of oxidizing methane to produce formaldehyde which comprises admixing methane with sulfur trioxide in proportions to provide from 0.2 to 15% of sulfur trioxide in vapor form in the mixture, and contacting the mixed gases with a contact mass comprising adsorptive silicious material while maintaining a temperature in the range from about 250 to about 450 C.

12. The method of oxidizing methane to produce formaldehyde which comprises admixing methane with sulfur trioxide in vapor form in proportions to provide from 0.2 to 15% of sulfur trioxide in the mixture, and contacting the mixed gases with a contact mass comprising activated charcoal while maintaining a temperature in the range from about 250 to about 450 C.

13. The method of oxidizing methane to produce formaldehyde which comprises admixing methane with sulfur trioxide in vapor form in proportions to provide from 0.2 to 15% of sulfur trioxide in the mixture, and contacting the mixed gases with a contact mass comprising activated alumina while maintaining a temperature in the range from about 250 to about 450 C.

14. The method of oxidizing methane containing gases to produce formaldehyde which comprises admixing the methane-containing gas with sulfur trioxide in vapor form in proportion to provide 0.2 to 15% of sulfur trioxide in the mixture and contacting the mixed gases with a contact mass comprising an adsorptive carrier and a compound of the metal of the class consisting of the transition elements and the elements of the Ib periodic group while maintaining a temperature in the range from about 325 to 425 C.

15. The method as set forth in claim 14, wherein the contact mass comprises an adsorptive carrier and a compound of cobalt.

16. The method as set forth in claim 14, wherein the contact mass comprises an adsorptive carrier and a compound of cerium.

17. The method of oxidizing methane containing gases to produce formaldehyde which comprises admixing the methane-containing gas with sulfur trioxide in vapor form in proportion to provide 0.2 to 15% of sulfur trioxide in the mixture and contacting the mixed gases with a contact mass comprising an adsorptive carrier and a compound of the transition elements and a compound of an element of the 11) periodic group While maintaining a temperature in the range from about 325 to about 425 C.

18. The method as set forth in claim 14 wherein the contact mass comprises an adsorptive carrier, a compound of cobalt and a compound of silver.

19. The method as set forth in claim 14 wherein the contact mass comprises an adsorptive carrier, a compound of cobalt and a compound of copper.

20. The method of oxidizing methane to produce'formaldehyde which comprises supplying a gaseous mixture including methane and sulfur trioxide in proportions to provide from 0.2 to 15% of sulfur trioxide in the mixture to a reactionzone to contact therein with a contact mass comprising an adsorptive catalytic material while'maintaining a temperature in the rangejfrom about 325 to about 425 0., separating formaldehyde from the resulting gaseous products, and returning the remaining gaseous products ,including unreacted methane and sulfur dioxide to said reaction zone to which the methane and sulfur trioxide are supplied to form the gaseous mixture entering said reaction zone for reaction therein.

21. The method as set forth in claim wherein theproportion of sulfur dioxide in the re action mixture is maintained below 60%.

22. The method as set forth in claim 20 wherein the proportion of sulfur dioxide in the reaction mixture is maintained below about 20%.

23. The method of oxidizing saturated aliphatic hydrocarbon gases to produce oxidation products which comprises supplying a gaseous mixture including such hydrocarbon gas and sulfur trioxide in proportions to provide from 0.2 to 15% of sulfur trioxide in the mixture to a reaction zone to contact with a contact mass comprising an adsorptive catalytic material while maintaining a temperature in the range from about 325 to about 425 C., separating aldehydic products from the resulting gaseous products, and returning the remaining gaseous products including unreacted hydrocarbon gas and sulfur dioxide to said reaction zone to which the hydro- 18 carbon gas and sulfur trioxide are supplied to form the gaseous mixture entering said reaction zone for reaction therein.

24. The method of oxidizing ethane to form aldehydic compounds which comprises admixing ethane with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising an adsorptive catalytic material of the class consisting of adsorptive carbonaceous, silicious and aluminiferous materials while maintaining a temperature in the range from about 270 to about 350 C.

25. The method of oxidizing butane to form aldehydic compounds which comprises admixing butane with sulfur trioxide in vapor form in the absence of free oxygen and contacting the mixed gases with a contact mass comprising silica gel while maintaining a temperature in the range from about to about 300 C.

WILLIAM H. REEDER, III.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,588,836 James June 15, 1926 1,985,875 Harter Dec. 25, 1934 2,066,622 Hasche Jan. 5, 1937 2,383,752 Sveda Aug. 28, 1945 OTHER REFERENCES Sabatier, Catalysis in Organic Chemistry, 1922, pages 102 to 103.

Marek and Hahn, The Catalytic Oxidation of Organic Compounds in the Vapor Phase, 1932, pages 12 and 13.

Berkman et al., Catalysis, pages 83 to 105, 1940, Reinhold Pub. Corp. 

1. THE METHOD OF OXIDIZING SATURATED ALIPHATIC HYDROCARBON GASES TO FORM PARTIALLY OXYGENATED COMPOUNDS CONTAINING RESIDUAL HYDROGEN INCLUDING COMPOUNDS CONTAINING THE CARBONYL GROUP WHICH COMPRISES ADMIXING SUCH GASES WITH SULFUR TRIOXIDE IN VAPOR FORM IN THE ABSENCE OF FREE OXYGEN AND CONTACTING THE MIXED GASES WITH A CONTACT MASS COMPRISING AN ADSORPTIVE CATALYTIC MA- 